Examples of image sensors used in portable terminals such as a camera module, include CMOS (Complementary Metal-Oxide Semiconductor) image sensors, CCD (Charge-Coupled Device) image sensor, etc. Among them, the CMOS image sensor has a relatively high degree of integration, and is thus easily produced on a large scale. As a result, CMOS image sensors are used in most mobile phone cameras, and are used in some low-priced digital cameras, as well. The CMOS image sensor has the advantage of being relatively inexpensive and requires relatively low power, but has a problem in that it is vulnerable to noise. Also, this noise is processed in such a manner as to use software to compensate for erroneous pixel values of the image provided by an image sensor.
In general, there is a limit on the frequency range of visible light perceivable by the human eye. The human eye can actually perceive a relatively small range of colors, especially at a low or high illuminance. Therefore, if noise removal is necessary, it may be performed with a scheme for reducing noise by reducing color information in an image at an extremely low or high luminance values of the image distribution, which the human eye has difficulty perceiving. Namely, in FIG. 1, a relatively low gain is applied to a color signal which has image information with a luminance equal to or smaller than Y1 or a luminance equal to or greater than Y2. In this scheme, it is usual that a process for reducing noise by reducing color information of an image (i.e., color desaturation) is performed after a process for removing the overall noise contained in the image (i.e., color noise reduction) is performed. In this case, if a luminance between adjacent areas rapidly changes, some pixels of the image are processed in monochrome. Therefore, a problem arises in that a gray spot is formed in the image.